Track type work machines are in widespread use in construction, mining, forestry, and similar industries. In particular, bulldozers, cranes and pavers are commonly seen track type work machines along roads, freeways and at construction sites. “Tracks” rather than wheels are typically used on work machines operating in environments where creating sufficient traction with conventional tires is problematic or impossible. Rather than rolling across a work surface on wheels, track type work machines utilize one or more tracks extending about a plurality of rolling elements. Such tracks are typically made up of a loop of coupled metal links having outer sides that engage the ground or work surface, and inner sides travelling about the rolling elements, which can include various drive rollers, support rollers, tensioners and “idlers.”
An idler in a track type work machine is a rolling element that passively rolls against the track and supports the inner side of the track as it rolls about the idler. Traditionally, idlers included a smooth cylindrical outer surface that rolled along rails defined by the individual track links, or by the idler itself. Newer designs, however, often include a plurality of teeth that engage against the bushings that join the track links, similar to a gear wheel.
While contemporary idler designs offer numerous advantages over traditional, non-toothed idlers, they have given rise to various new problems and engineering challenges. Over the course of work machine operation, debris can more readily find its way between a toothed idler and track links than in a traditional design. As a result, debris such as a rock can actually become lodged between a portion of a track link and the teeth, or pockets between the teeth, of the rotating idler. Similar problems are associated with the toothed sprocket and track on the roller frame opposite the idler.
Lodging of a rock between the idler or sprocket and the track can effectively lengthen the distance traversed by the track, and/or increase the tension thereof having two possible outcomes. First, if the work machine track components are sufficiently robust, the rock will be crushed. Alternatively, the rock may actually strain the track and associated components to the point at which something breaks.
In an attempt to avoid the rock-crushing, track-breaking alternatives, designers have developed a variety of means to allow debris to simply roll through, for example by actually recoiling the idler, to lower or maintain the track tension. One design incorporates a coil spring with the track roller frame. The coil spring is positioned such that it can absorb recoil forces on the idler, such as while a rock is lodged between the idler or sprocket and the track. In general, it is desirable to limit the frequency of recoil events in the track system, as they tend to lead to excessive wear of the components. With a coil spring, recoil frequency would generally be limited by utilizing a coil spring having a relatively high spring constant such that it will only be compressed when a recoil force above a certain threshold is encountered.
While such a design is relatively simple, a particularly large, heavy-duty coil spring can be necessary to provide sufficient resistance to recoil.
In many work machine designs, known coil springs having a sufficient spring constant may not actually fit into the track roller frame, therefore being difficult or impossible to utilize. Such coil springs must also typically be surrounded by a steel structure on the roller frame for safety and protection of the spring itself. Further still, coil springs made of common known materials may not have a sufficiently linear spring force as a function of the degree of compression. In other words, it may become exceedingly difficult to further compress a coil spring when it is close to full recoil, confounding its intended purpose.
In recent years, designers have proposed various alternatives to the aforementioned coil spring designs, some meeting with significant success. One example of a non-coil-spring idler recoil design incorporates a combined pneumatic and hydraulic system to absorb loads on the idler. In such a design, recoil forces on the idler are absorbed by displacing hydraulic fluid, and simultaneously compressing gas in an accumulator. While these more modern designs offer certain advantages over coil spring designs, they must typically be connected with the work machine hydraulic system, requiring hydraulic lines to extend between the track assembly and the work machine body, a design that is both complex and apt to require frequent maintenance. One particular design utilizes a gas accumulator mechanically linked with the idler to absorb recoil forces thereon. U.S. Pat. No. 6,682,155 to Hoff, et al. is directed to one such system. Hoff, et al. describe a track tension adjustment actuator, operable to selectively reduce tension on the idler wheel in a track type work machine, especially when the work machine is traveling. The actuator of Hoff, et al. includes a hydraulic cylinder housing, and a recoil piston disposed within the cylinder housing and coupled with the idler wheel. The cylinder housing and recoil piston form a recoil chamber that is pressurized to urge the recoil piston away from the work machine drive wheel, tensioning the track. Another known design is described in U.S. patent application Ser. No. 10/325,362, now abandoned. The '362 disclosure is directed to a track tension adjustment mechanism, in particular a system, like Hoff, et al., wherein tension on an idler wheel of a track type work machine is reduced when the machine is traveling. The '362 disclosure includes a track tensioning system having an idler wheel, a drive wheel, and a drive track. A hydraulic motor is operable to advance the drive wheel, and an actuator having a recoil chamber is coupled with the idler wheel to urge the idler wheel away from the drive wheel and thereby tension the track. A controlled quantity of hydraulic fluid may be delivered to the actuator to adjust the track tension as needed.
While the above systems offer various advantages, particularly in that a relatively smaller, simpler recoil system can be made, high pressure gas accumulators have inherent sealing problems, particularly where they are subjected to side loads on pistons therein.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.